The present invention relates to a system for digitally converting a time multiplex signal into a frequency multiplex signal and vice versa, i.e. a transmultiplexer. More particularly the present invention relates to a system for the digital conversion of a time multiplex signal into a frequency multiplex signal wherein the signals of the individual time multiplex channels are filtered by means of respective bandpass filters, their sampling rates are increased by the factor N to fA and the output signals of these bandpass filters are combined, by means of a summing member, into the frequency multiplex signal, and/or to a system for the digital conversion of a frequency multiplex signal into a time multiplex signal, wherein the digitalized frequency multiplex signal is divided by means of respective bandpass filters into the signals of the individual multiplex channels and their sampling rate fA is reduced by the factor N.
Such a digital transmultiplexer is described in the paper by Carl F. Kurth et al, entitled "Per-Channel, Memory Oriented Transmultiplexer With Logarithmic Processing--Architecture and Simulation" published in International Conference on Communications, IEEE, 1981, pages 7.3.1 to 7.3.5.
In this known transmultiplexer a minimum phase filter (FIR) having 434 delay member branches is required for every channel as the digital bandpass filter for interpolation or decimation so as to realize the desired frequency response characteristic (page 7.3.2, left-hand column, second paragraph).